If you connect to multiple sites or are a transport or service provider for multiple sites that are using private IP addresses meaning some may overlap and/or be the same (e.g. 10.10.10.0 for customer A and B) what would be the best options in terms of routing. Let's say your infrastructure is small meaning maybe you don't want to do a mbgp/mpls backbone type infrastructure if you only have a couple devices or something, would perhaps configuring vrf light route leaking be the best way to go?
Would still just building an mpls infrastructure still be best option if lets say you only have 2 routers meaning I guess they act as PE and LSR (if that is even supported)?
Also, what if you have IPSEC tunnels or something and you infrastructure is using the same subnet the remote end is using or wants to use such as 10.10.10.0 /24 what would be the best options as to my knowledge that would not be supported unless I am mistaken??
Awesome Francisco yes it does make sense.
So basically, if let's say you have an existing network that provides services as I mentioned, however right now the network is small as I mentioned (idk like 1 router and 1 switch), but you want to be able to scale easily and/or more efficient if needed in the future, I am just trying to decide what the best type of implementations would be - yes I was thinking just to go ahead and do mpls with MBGP instead of let's say VRF light or something. What other good scalable options you mentioned would there be besides these?
Also when you say shared zone, are you talking about let's say systems that must be accessed by these customers (DNS, Apps, etc.) and not between two remote customers who must communicate correct?
You ask 2 questions and the second one is easier, so let me start with it. If you have ipsec tunnel or something to a peer and that peer has a subnet that is the same as a subnet in your network such as 10.10.10.0/24 then one side or the other must do address translation. I have worked with customers in this type situation and while we normally think of not translating site to site vpn traffic it is certainly a supported feature to translate that traffic. I have done it and it works.
I am less clear about your first question. If you are a service provider or a transport provider I would think that it would be a priority to implement something that scales effectively. And something like vrf lite is probably not such a good choice. If you have a fairly small infrastructure perhaps something like GRE tunnels, or perhaps multi-point GRE might allow you to connect sites and have them communicate private address to private address. But as part of this question you bring up the possibility that customer A and customer B might be using the same private IP subnet. In that case one (or both) will need to do address translation (or you might need to do the translation for them).